1. Technical Field
The present disclosure relates to an apparatus for balancing voltages of a direct current (DC) link capacitor of an inverter.
2. Description of the Related Art
Generally, an inverter is an apparatus for receiving an alternating current (AC) power, rectifying the AC power into direct current (DC) power, and outputting AC power having a desired frequency and a desired magnitude. At this point, a smoothing electrolytic capacitor is connected to a DC link of a rectification unit of the inverter.
When an inverter is a type having an input voltage of 400V, a voltage being charged at an electrolytic capacitor of a smoothing unit is about 500V to 800V. However, because a rated voltage of a conventional electrolytic capacitor is 400V, when a smoothing unit of an inverter having an input voltage of 400V is designed, an equivalent rated voltage of the smoothing unit is designed to have 800Vdc by connecting electrolytic capacitors in series.
FIG. 1 is a configuration diagram for describing a conventional inverter.
A smoothing unit 200 is configured with electrolytic capacitors 210, 220, 230, and 240 for smoothing AC power rectified by a rectification unit 100, and voltage divider resistors 215, 225, 235, and 245 which are connected in parallel to the electrolytic capacitors 210, 220, 230, and 240, respectively, and a voltage charged in the smoothing unit 200 is applied to a switching element (not shown) of an inverter unit 300. At this point, two electrolytic capacitors and two voltage divider resistors are connected in series to each other.
The smoothing unit 200 of such a conventional industrial inverter has a structure in which an electrolytic capacitor and a voltage divider resistor are connected in series and in parallel as shown in FIG. 1 so that a single capacitor is necessary for a single voltage divider resistor. An inverter using a plurality of electrolytic capacitors needs voltage divider resistors corresponding to the number of the electrolytic capacitors so that there are problems in that space for mechanically accommodating the electrolytic capacitors and the voltage divider resistors is required and a manufacturing cost is increased as the number of the voltage divider resistors.
Also, a leakage current always occurs at an electrolytic capacitor through a voltage divider resistor so that there is a problem in that efficiency of an inverter is reduced.
Meanwhile, when a voltage of the smoothing unit 200 is not equally applied to capacitors that are connected in series to each other, a voltage over a rated voltage (for example, 400V) may be charged at a specific capacitor. In this case, the capacitor explodes so that there are problems in that an inverter is damaged and also risk of fire is increased due to an electrical spark generated when the capacitor explodes.